书城教材教辅科学读本(英文原版)(套装1-6册)
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第100章 第二册(17)

He put in seven spoonfuls of the lime, but by the time he had done there was a great heap of wet lime at the bottom. The water too was flowing over the top of the glass.

They waited till the water was clear. Then they poured it out into another tumbler. To make sure there were no solid bits of lime in the water, they made it filter through blottingpaper.

"Now look," said Fred, "I am going to breathe into the water through this straw. If there is any lime dissolved in it, the water will turn white like milk as I breathe into it.

"See, it looks quite milky already," he added. "The water has got some lime in it. All the lime did not sink to the bottom of the tumbler. Some of it was dissolved. Water dissolves a large quantity of salt, but only a little lime."SUMMARY

When a substance dissolves in water, it breaks up into little morsels, which ?nd their way into the pores of the water. The water cannot dissolve any more after the pores are all ?lled.

Starch

"What is this, Norah?" asked Fred.

"It is some of the starch that mother uses tomake your collars stiff." said Norah.

"Well, I want to have a chat about starch this evening." said Fred.